NORTHBRIDGE 
To many, the severe weather may seem like another unfortunate Halloween weather prank, but to those studying northern saw-whet owls, Mother Nature is giving something of a bonus to an already active year.

A bad storm this time of year delays saw-whet owl migration, but when the weather lets up, scientists may have more birds than they can handle.

“We've had some of our biggest nights after a long series of weather delays,” bird bander Strickland Wheelock explained.

Mr. Wheelock runs the Uxbridge owl banding station out of his home. For the past decade his group has been catching northern saw-whet owls on their migration south, inspecting them, banding them and sending them back on their way. This year is a good year that may soon get better.

The owls tend to migrate this time each year, but a bad storm halts the migration in its tracks, with the birds settling down in shelter until the storm passes. They continue their journey when the wind and precipitation subside. Once the storm passes, it can be like floodgates releasing the water behind them.

But even without the storm, Mr. Wheelock said, the Uxbridge station and its sister station in Lincoln have been seeing a complete reversal from last year, when saw-whet owl populations collapsed.

“This has just been an exceptionally good season,” he said. “The migration has been incredible.”

Mr. Wheelock said he has been banding birds since 1972, and the Uxbridge reporting station has been active for a decade and the Lincoln station for seven years.

“This has definitely been one of our best years,” he said.

With 300 birds caught and banded between the two stations, the numbers are already nearly double from last year, one of the worst saw-whet owl migration years in recent memory.

Northern saw-whet owls are tiny docile owls that migrate each fall from as far north as northern Ontario south into Maryland and Virginia. Officials believe there are between 100,000 and 300,000 in the United States and Canada.

The owls, according to Mark Lynch of Worcester, one of the region's many skilled birders, migrate at night across a broad front, holing up during the day and continuing their flight south when it gets dark again. They are not often seen, choosing dense habitat to hide in during the day. Still, they are occasionally killed by larger owls and other birds of prey. Saw-whet bands have been found in pellets of barred and great horned owls.

Mr. Lynch said the birds mostly breed in the north, but some breed in Massachusetts.

“There are some breeding pairs in the hill towns in northern Central Massachusetts,” he said.

The tiny owls eat mostly white-footed mice, but also an occasional vole or other small mammal.

The birds are difficult to find during the day because they hide well in thick trees and bushes. If you stumble on one, it is a treat. They will not fly away, but sit there watching you. People have been known to walk up to saw-whet owls and pick them up with no objection by the owl. Mr. Lynch said he does not recommend it because it is not good for the birds to be handled too much by humans.

Owls are among the least seen birds but a major treat for birders.

“It is never a bad day when you see an owl,” Mr. Lynch said.

There are many screech owls in the region, and occasional sightings of the larger barred and great horned owls. It is a special occasion if a majestic snowy owl makes its way down to the area from the north, and it is a banner day when there is a very rare sighting of the huge gray owl.

Banding of the saw-whet owls takes place to help gain better understanding of the birds, about which less is known than about any other common owl. One unknown is why the owls tend to come in big numbers in four-year cycles. Mr. Wheelock said it could be weather or availability of food supply that causes numbers to grow.

This year there are not only many more birds, but the unusual number is happening outside the usual cycle. The last saw-whet boom was three years ago.

To catch the birds, Mr. Wheelock said, banders set up nets during the fall on Lookout Rock in Northbridge and in Lincoln. The nets are similar to what is used to catch chickadees and other small birds, because saw-whet owls are so small. At dusk the banders go out to check the nets. This year they have been rarely disappointed.

At the site where the nets are set up, space is limited and visitors are allowed to join the banding effort by reservation only.

Mr. Wheelock said banders welcome the chance to offer the educational component they can provide through the banding, but they need to keep groups small. Visitors joining them have been mostly from high schools, colleges and various bird clubs.

The banding continues as long as owls are being caught or until participants get tired, usually between 10 p.m. and midnight. This year the weather has been relatively mild. Some years banders have sat in snow waiting for the owls to arrive.

When banders find birds, they weigh them, measure their wingspan and check their feathers to determine sex and age. Mr. Wheelock said the banders mostly find females because they use the call of a male saw-whet owl played over and over to attract the females down from 500 to 1,000 feet in the sky as they pass through the area.

“The females we're getting this year are over the chart limits,” he said. “They are just big females.”

The banding helps researchers learn more about the understudied species. With stations banding birds as far north as northern Ontario and as far west as the Midwest, banders are beginning to compile a large database of the many birds that pass through each year.

Occasionally the Uxbridge station catches a bird it has already banded heading south again. Sometimes its birds show up at other stations. It is not a common find. For every 100 birds that show up in nets, two or three have been banded elsewhere. This year a previously banded bird was seen in Lincoln.

The small owls are pretty easy to lure: In one case in Lincoln, the attraction of the male call was enough to lure one female into the nets four times. Occasionally a screech owl or barred owl is caught in the nets.

The birds also tend to be charming. They are docile to the point where, when the banders go to release them, the owls will perch on their arm for 10 to 15 minutes before flying away. One volunteer placed one of the birds on her shoulder after processing it and it stayed there for about a half-hour watching the banders study its cousins.

The banding effort will continue through the late fall until the birds are no longer being found. Once that is done, the data are shared with other banders and with the U.S. Geological Survey's bird banding laboratory in Maryland.